Central nervous system involvement during HIV-1 infection represents one of the most serious complications beyond the induction of immunodeficiency. The penetration of HIV into the brain not only carries the potential for the development of serious neurological disease but may lead to the establishment of unique viral reservoirs protected from antiretroviral therapies. This compartmentalization and neurotoxicity may depend on the emergence of brain-specific quasispecies over time. The proposed studies will use heteroduplex tracking assay (HTA) technology to provide a critical evaluation of the extent to which HIV-1 and SIVsm evolve in the context of systemic and CNS disease. Viral envelope gene sequences will be evaluated in matched postmortem samples of plasma, cerebrospinal fluid (CSF) and various brain regions from individuals with severe neurological disease and contrasted with samples taken from individuals with comparable systemic disease but no neurological complications. A longitudinal analysis of SIVsm evolution in plasma and CSF will be used to provide an indication of co-evolution or divergent evolution within these compartments over time. Viral species that emerge within plasma and CSF will then be contrasted with sequences in brain and lymph nodes at autopsy. Full-length envelope genes unique to various regions of encephalitic brains will then be cloned, identified using envelope-specific HTA, evaluated for co-receptor use in PBMCs and macrophages and used to prepare full length, recombinant gp120. The purified gp120 will then be tested for neurotoxic properties in primary cortical and microglial cultures using assays of cell death, measures of neuronal calcium destabilization and quantification of the secretion of cytokines, chemokines and putative neurotoxins. After identifying envelope sequences that are neuropathogenic, gene array technology will be used to determine the profile of gene expression that is unique to the stimulation of microglia/macrophages by those sequences. SIVsm with an envelope gene representing a unique, compartmentalized neuropathogenic species will then be used to infect three macaques and the course of infection monitored in plasma and CSF. Results from these experiments will identify the nature of lentiviral envelope sequences that allow the development of unique viral reservoirs within the brain and will begin to answer how such sequences provoke toxic inflammatory reactions and neuropathogenesis. [unreadable] [unreadable]